1. Field of the Invention
This invention relates to a double chuck type mechanical pencil provided with a rear chuck for drawing out a lead in a fixed amount having a chuck ring loosely fitted thereon, and a front chuck for preventing a lead from retreating.
2. Description of the Prior Art
Conventionally, various double chuck type mechanical pencils have been proposed for mainly reducing a loss of a lead. However, in the double chuck type mechanical pencil of this kind, where a lead is held by two chucks, when one chuck is rotated for some reason, the held lead is twisted and becomes broken. In such a case as described, chips of the broken lead remain in and between the front chuck and the rear chuck to disturb the drawing-out of a lead, and when a posterior lead is pushed out after the preceding lead was broken, the broken chips of the preceding lead are deviated from the posterior lead, thereby making it impossible to draw out the posterior lead.
For overcoming such an inconvenience as described above, a double chuck type mechanical pencil has been proposed in which a rear chuck cannot be rotated, as disclosed in Japanese Patent Laid-open No. Hei 7-228087, for example.
Referring now to FIG. 1, there is illustrated the double chuck type mechanical pencil disclosed in the above publication. The double chuck type mechanical pencil comprises a tip member 22 provided in the front portion of an axial tube 21, an end chuck 25 incorporated in the tip member 22 and biased rearward in a longitudinal direction by means of a front spring 23 to hold a lead 24, and a draw-out chuck 26 positioned rearward in a longitudinal direction from the end chuck 25 to draw out the lead 24, wherein a connector 28 connected to the draw-out chuck 26 can be slidably moved in a longitudinal direction but cannot be rotated with respect to an inner sleeve 27 connected to the tip member 22.
More particularly, axially extending key ways 27a are formed in the inner sleeve 27, keys 28a of the connector 28 are engaged with the key ways 27a to make the draw-out chuck 26 unrotatable, and the lead 24 held between the end chuck 25 and the draw-out chuck 26 is prevented from being twisted and snapped off.
In the conventional mechanical pencil as described above, however, particularly where the tip member is formed of synthetic resin, the end chuck collides with the extreme end of the tip member during use to wear that portion, resulting in inaccuracy of fitting relative to the end chuck and raising the possibility that the mechanical pencil becomes inoperative.
Further, where the tip member is prepared with a metal having abrasion resistance, the construction of the tip member becomes complicated so that it takes time to finish an opening diameter of the tip member with accuracy by plating, etc., in terms of the outside diameter of the end chuck. Further, since a large tip member is bored to form an opening, a burr tends to occur in the opening. Accordingly, there occurs an inconvenience that accuracy of the opening diameter is low and it takes time to remove the burr so that cost increases.
Furthermore, according to the prior art, for eliminating snapping-off of a lead held between both the chucks caused by twisting thereof, detent of the rear chuck and locking or adhesion between the tip member and the axial tube are necessary, which parts are complicated in construction, posing an inconvenience that it takes time to manufacture and assemble parts, increasing the cost.